Renal preservation, the ex vivo storage of cadaveric kidneys, is a relatively new field. Preservation of cadaveric kidneys for transplantation is common practice in hospitals; however, advances have been limited to trial and error experimentation. Although this approach has been partially successful from a clinical standpoint, the actual principles behind these successes are not well understood.
As renal transplantation has evolved from a strictly research procedure to an esablished clinical therapy for end-stage renal disease, renal preservation has progressed from the laboratory research stage to an established clinical method. At present, the two most commonly used methods for renal preservation are simple hypothermic storage and continuous perfusion. With simple hypothermic storage, the most common method of clinical renal preservation, the organs are removed from the cadaver doner and are cooled rapidly. This is usually achieved by a combination of external cooling and a short period of perfusion to drop the core temperature as quickly as possible. The kidneys are then stored, immersed in a flush-out solution in a simple plastic container, and kept at a temperature of 0.degree. to 4.degree. by immersing the container in ice. The advantages of this method are its simplicity, its low cost, and the ease of transportation of the organs. The composition of the flush-out solution to provide optimum preservation has been extensively studied.
The second method of renal preservation which has undergone extensive laboratory investigation, as well as clinical testing, is continuous pulsatile perfusion. The basic ingredients of continuous perfusion are (1) pulsatile flow, (2) hypothermia, (3) membrane oxygenation, and (4) a perfusate containing both albumin and lipids. With minor modifications, all presently used clinical preservation units share these basic principles. There are several advantages to continuous perfusion in clinical transplantation. First, perfusion provides enough time to make cadaveric transplantation a partly elective procedure. Second, it allows viability testing prior to implantation. A significant improvement in the results of cadaveric renal transplantation could be expected if the preservation time could be extended to the 5 to 7 days required for present methods of mixed lymphocyte culture testing.
The ability to successfully preserve human kidneys for two to three days by either simple cold storage after initial flushing with an intracellular electrolyte solution or by pulsatile perfusion with an electrolyte-protein solution has allowed sufficient time for histo-compatibility testing of the donor and recipient, kidney sharing among transplant centers, careful preoperative preparation of the recipient, time for preliminary donor culture results to become available, and vascular repairs of the kidney grant prior to implantation. Kidneys preserved for 72 hours using hypothermic pulsatile perfusion with cryoprecipitated plasma proved to be a significant advance for human kidney preservation and is currently the preferred method of preservation. Kidney organ preservation with ice-cold intracellular electrolyte flush solution followed by simple cold storage has been satisfactorily employed for human kidney preservation for up to 61 hours.
Serum albumin, in various forms, is used exclusively for clinical organ preservation to produce the necessary oncotic pressure. These forms include cryoprecipitated plasma, plasma protein fraction, human serum albumin, and silica gel-treated plasma. However, because these perfusates are prepared from naturally derived materials, variation is unavoidable. It would be particularly advantageous if a perfusate containing a synthetic colloidal was available.
In the past, a large number of synthetic colloidal materials have been experimentally tested for effectiveness in kidney preservation. These colloids include dextrans, polyvinyl pyrrolidine, pluronics, hydroxyethyl starch (HES), Ficoll, gum arabic, and polyethylene glycol. None of these were as effective as serum albumin. However, HES was effective for 24 hours of preservation and in some cases for 72 hours of preservation. These colloidal materials were all tested in saline-based perfusates. Recently, excellent 72-hour preservation of canine kidney was observed with a perfusate containing gluconate anions in place of chloride with human serum albumin (HSA) for colloidal osmotic support.
In accordance with the present invention a method of preserving kidneys using a perfusate containing HES in place of human serum albumin is disclosed.
As indicated hereinabove, serum albumin (HSA) based perfusates have been the standard for preservation of kidneys both experimentally and clinically for the past 17 years. Unfortunately preservation periods of only three days could be obtained with these types of perfusates. Although both of these methods preserve kidney viability for up to three days, longer preservation times are difficult to obtain consistently. Moreover, even though these methods preserve viability for up to three days, the kidneys are damaged as indicated by the elevated post-transplantation serum creatinine levels and time required to return those elevated levels to normal. Early perfusates were chosen from electrolyte solutions readily available for intravenous infusion and were basically of extracellular composition.
Heretofore, acceptable methods for renal preservation have not been available. Those that have been proven clinically effective are limited to short-term-storage (three days) and significantly reduced viability. The present invention describes the biochemical composition of the perfusate best suited for the hypothermically perfused kidneys and a novel synthetic colloidal osmotic agent that yields significantly improved long-term preservation.